This invention relates to a method for producing an article which includes a fluid passage such as for cooling, and, more particularly, to a method for making a turbomachinery article such as a blading member.
A variety of elevated temperature operating gas turbine engine components, including blades and vanes, have employed fluid-cooling, particularly air. Such cooling enhances the ability of such a member to withstand operation at temperatures in excess of those at which the component's material of construction can operate effectively without such cooling. As gas turbine engine blade design has advanced, the cooling passages within such a component have become increasingly complex. Typical of such air-cooled turbine blades and vanes are those shown in U.S. Pat. Nos. 3,628,880-Smuland et al and 3,628,885-Sidenstick et al, the disclosures of which are incorporated herein by reference. As shown by these and other publications, current air-cooling of blades and vanes is accomplished by a complex internal cooling passage, generally with holes in a wall connecting the internal passage with the blade or vane outer surface such as for film cooling.
While it is difficult to manufacture such complex structures in relatively large blades and vanes used in the larger gas turbine engines, it is extremely difficult and very costly to provide such complex cooling passages within small blades and vanes, for example for use in gas turbine engines which power helicopters or relatively small aircraft.
Currently such turbine blades and vanes are manufactured predominantly by precision casting techniques involving the use of removable casting cores which are complex in shape, difficult to manufacture accurately, difficult to handle and difficult to maintain in position during the casting process. Such cores are generally ceramic in nature and core breakage has been a common type of failure in these processes. Other problems have resulted from core shift, sag, or both, as a result of the high temperatures and sometimes relatively long holding times involved in such a casting operation. Such casting problems have reduced the efficiency of casting and thereby increased the cost of the cast article.